1. Field of the Invention
The present invention relates to a method and apparatus for the tuning of resonant circuits of a communications receiver, and in particular of television and radio receiver apparatus with an oscillator circuit employing a phase-locked loop system and a mixing stage for generation of an intermediate frequency, where in the course of tuning of the receiver apparatus the individual filter circuits are balanced to optimum values and the determined tuning values are coordinated to voltage-variable diodes of the individual filter circuits.
2. Brief Description of the Background of the Invention Including Prior Art
A tuner unit is known from German Patent Application Laid Open DE-OS No. 2,854,852, which automatically tunes the high frequency circuits employing a phase-locked loop tuning system and employing three auxiliary oscillators and analog storage units coordinated to the oscillators. Here a number of auxiliary oscillators, corresponding to the number of high frequency circuits to be balanced, is required. The number of the necessary auxiliary oscillators and thus the materials requirements increase particularly in that case if for example for a television receiver Band I, Band III, and the bands IV and V are to be balanced. The danger of ambiguities exists between the frequencies of the tuner oscillator, of the auxiliary oscillators and of the receiver frequencies. It is disadvantageous for a practical realization of the proposed tuning unit that the exciting coil windings of the auxiliary oscillators can cause undesired resonances and damping effects, which in addition cause an uncontrolled mistuning of the circuits, if the auxiliary oscillators are turned off after performance of the balancing. In addition, analog storage provisions are furnished, which have to be reloaded at time intervals in order to obtain optimum tuning values. For these reasons an optimum balancing of the receiver apparatus cannot be obtained. In addition, disturbances on the screen or in the speaker become visible or, respectively, can be heard, caused by the frequently repeating of the fine tuning.
A tuning method for radio receivers is described in the journal "Nachrichten elektronik", issue 11, 1979, pages 365-368 which also employs additional auxiliary circuits in the high frequency filters. Here again disadvantageous influences on the circuits occur during operation of the tuned receiver. As the left and middle column on page 367 indicate, the accuracy of the tuning based on special devices is achieved only based on exactly paired diodes. This again requires expenditures which cannot be neglected.